1. Field of the Invention
The present invention relates to a frequency multiplier for use in a local oscillator and to a wireless device incorporating the same.
2. Description of the Related Art
A known prior art frequency multiplier provides an output having a frequency which is an integral multiple of an input signal by generating harmonic components by operating a transistor as a Class-C amplifier.
FIG. 6 is a circuit diagram showing a schematic structure of a prior art frequency multiplier. A frequency multiplier 50 includes an input terminal 51 for inputting an input signal, a front-stage coupling circuit 52, a terminal 53, to which a positive power supply is connected, a transistor 54, a final-stage coupling circuit 55, and an output terminal 56.
In the frequency multiplier 50, firstly, an input signal of a frequency xcfx89, which is input from the input terminal 51, is input to the transistor 54 via the front-stage coupling circuit 52. The transistor 54 is not used for amplification in its linear region, as in typical cases. It is employed in a Class-C operation using a small bias or no bias. As shown in FIG. 6, when using a Si bipolar transistor as the transistor 54 with its emitter grounded, almost no collector current flows unless the base voltage is higher than 0.6 V. As a result, since the portion of the input waveform during which the collector current flows is limited, the output waveform from the collector is distorted to include harmonic components. The signals output from the collector of the transistor 54 are output from the output terminal 56 via the final-stage coupling circuit 55.
In the prior art frequency multiplier having a transmitter driven in Class-C operation the collector efficiency (the ratio of the collector current to the emitter current) of the transistor is low. A limitation is that the frequency in a single frequency multiplier is multiplied by a factor of four at most. When the multiplication factor is larger, the number of stages of frequency multipliers must be increased. As a result, the size of the component increases, which leads to higher cost.
To overcome the above described problems, embodiments of the present invention provide a compact frequency multiplier capable of performing high-degree multiplication and a wireless device incorporating the same.
One embodiment of the present invention provides a frequency multiplier including a first resonant circuit resonating with the frequency of an input signal, a second resonant circuit and an idler circuit both resonating with a frequency n times that of the input signal, and a variable reactor. The first and second resonant circuits are connected in series between an input and an output, and a parallel circuit constituted of the idler circuit and the variable reactor is connected in parallel between the input and the output so as to form a current-excitation frequency multiplier. The idler circuit is contained in a multi-layer substrate formed of a plurality of dielectric layers, on which the variable reactor is mounted.
According to the above described frequency multiplier, since the idler circuit constituting the frequency multiplier is contained in the multi-layer substrate, the idler circuit can have a high Q value. Thus, a high-efficiency frequency multiplier can be produced. Also, high-degree multiplication can be achieved while maintaining high efficiency.
Another embodiment of the present invention provides a frequency multiplier including a first resonant circuit resonating with the frequency of an input signal, a second resonant circuit and an idler circuit both resonating with a frequency n times that of the input signal, and a variable reactor. The first resonant circuit and the second resonant circuit are connected in parallel between an input and an output, and a parallel circuit constituted of the idler circuit and the variable reactor is connected in series between the input and the output so as to form a voltage-excitation frequency multiplier. The idler circuit is contained in a multi-layer substrate formed of a plurality of dielectric layers, on which the variable reactor is mounted.
According to the above described frequency multiplier, since the idler circuit constituting the frequency multiplier is contained in the multi-layer substrate, the idler circuit can have a high Q value. Thus, a high-efficiency frequency multiplier can be produced. Also, high-degree multiplication can be achieved while maintaining high efficiency.
In addition, since this frequency multiplier is a voltage-excitation type, higher-degree multiplication can be performed by utilizing a higher-mode excited frequency.
In the above described frequency multipliers, at least one of the first resonant circuit and the second resonant circuit disposed in one of the above-described frequency multipliers may be contained in the multi-layer substrate. Thus, variations in the frequency of the tuning circuit can be suppressed. Accordingly, a frequency multiplier having better characteristics can be produced.
Yet another preferred embodiment of the present invention provides a wireless device which incorporates one of the above-described frequency multipliers.
The above-described wireless device can perform high-degree multiplication with a single unit and has high efficiency, with the result that the size of the wireless device can be reduced and high efficiency is obtainable.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.